MPlayer 学习应用笔记(0)

• FourCC
• A Guide To Developing MPlayer Codes
• 播放器一般原理

记录研究MPlayer源码过程中获得的零散知识点

FourCC

FourCC全称Four-Character Codes, 即四字节代码，其实就是：

typedef unsigned in FourCC

音视频播放软件通过查询与FourCC代码相关联的音视频解码器来播放特定的音视频流。 比如DIV3=DivX Low-Motion, DIV4=DivX Fast-Motion

#define MAKE_FOURCC(a,b,c,d) \
(((uint32)d) | ((uint32)c << 8) | ((uint32)b << 16) | ((uint32)a << 24))
...
switch(val){
	case MAKE_FOURCC('f', 'm', 't', ''):
		...
		break;
		
	case MAKE_FOURCC('Y', '4', '4', '2')
		...
		break;
		
	...
}

通过上面程序可以看出来，一般使用宏生成FOURCC.

A Guide To Developing MPlayer Codes

– by Mike Melanson, who has developed a number of open source decoders for the MPlayer.

Points:

1. If the encoded data is stored in a media file format that MPlayer doesn’t understand, then you will either need to somehow convert the format to a media file format that the program does understand, or write your own MPlayer file demuxer that can handle the data.
2. vv

Step:

1. Modify the local copy of codecs.conf.
2. Follow the ad_sample.c or vd_*.c to create a new source file which contains the main decoding function that MPlayer will call to decode data.
3. Modify the Makefile so that it will compile your new source file.
4. Add your codec to the array in ad.c or vd.c.

播放器一般原理

Source filter -> 
	Demux filter ->
        -->Video Decoder filter  
				-> Color Space Converter filter
					->Video Render filter
					
		-->Audio Decoder filter
			->Audio Render filter
					

Demux filter:

1. 解复用过滤器的作用是识别文件类型，媒体类型，分离出各种媒体原始数据， 打上时钟信息后送给下级decoder filter.
2. 为了识别出不同的文件类型和媒体类型，常规的做法是读取一部分数据，然后遍历解复用过滤器支持的文件格式和媒体格式， 做匹配来确定是哪种文件类型，哪种媒体类型。